Biofouling is the undesirable accumulation of micro-organisms, plants, and animals on artificial surfaces immersed in water such as ship hulls, docks, buoys, etc. More than 4000 organisms having been reported as being species causing biofouling, including bacteria, micro-algae, macro-algae, sea-grass, molluscs, crustacean, etc. Most fouling-causing organisms have a swimming larval stage followed by a sedentary adult stage that remains attached to its substratum throughout the remainder of its life. The attached adult organisms can increase frictional resistance on the hulls of ships, increase the weight of buoys, increase oil flat loading weight, block seawater pipes, decrease water exchange through aquaculture net boxes, and compete for space and food with cultured shellfish, among other negative effects.
The global economic costs due to biofouling are extremely large. For example, biofouling of ships' hulls leads to the high frictional resistance, increase of weight, and subsequent potential speed reduction and loss of maneuverability. As a result, higher fuel consumption is needed, causing increased emissions of harmful compounds. It may also entail a need for heavier and energetically efficient machinery. The estimated economic loss caused by biofouling is around US$ 6 billion annually. The use of a typical antifouling agent (tributyltin) on ship hulls, has saved the US Navy an estimated US$150 million each year. Because of these large-scale economic consequences, development of efficient antifouling methodologies is crucial.
Traditionally, antifouling materials are metal based. Prior to the 17th century, plumbum was the most common antifouling agent. From 1960's until recently, organotins, represented by tributyltin (TBT), were common anti-fouling agents. However, environmental concerns over the effect of organotins first arose in France, where severe problems were encountered in commercial oyster fisheries in areas where there was intense boating activity and poor tidal exchange. Since then, the distribution, fate and effects of organotins and other antifoulants on the marine and freshwater environment have been under intense scrutiny. Research suggests damaging effects of organotins on reproduction and growth of various marine life. In addition, TBT is known to threaten non-target organisms in the marine ecosystem, causing dramatic effects on shell fishes by inducing imposex in large populations. At concentrations as low as 1 ng/L, TBT can induce imposex. Now, TBT is regarded as one of the most toxic and hazardous compounds introduced into marine environments. In response to these concerns, the Marine Environment Protection Committee (MEPC) of the International Maritime Organization (IMO) has implemented a ban on the application of TBT paints from 1 Jan. 2003, with the intent that no TBT paints will remain on vessels after 1 Jan. 2008.
As an alternative, vessels are increasingly painted with copper-based paints. However, copper-based paints also have negative effects on the marine environment. For example, oysters accumulate considerable amounts of copper and copper is toxic to marine algae.
The toxicity concern is not only about TBT, but about all existing antifouling biocides, and has thus stimulated research and development of non-toxic antifouling coatings. The development of a marine paint or paint ingredient that is non-toxic, non-heavy-metal-based, and benign to the marine environment is urgently sought. The present invention provides a novel category of antifouling compounds which are nontoxic and environmental friendly.